Fluids comprising zirconium isopropylamine crosslinking agents and associated methods

ABSTRACT

Treatment fluids that may comprise an aqueous fluid, a gelling agent, and a zirconium triisopropylamine crosslinking agent are provided. Also provided are crosslinking agents that may comprise a zirconium triisopropylamine crosslinking agent, and a zirconium IV-containing crosslinking agent.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention is related to copending U.S. application Ser. No.______ [Attorney Docket No. HES 2004-IP-015962U1] entitled “FluidsComprising Zirconium Isopropylamine Crosslinking Agents and AssociatedMethods,” filed concurrently herewith, the entire disclosure of which isincorporated herein by reference.

BACKGROUND

The present invention relates generally to the treatment of subterraneanformations with crosslinked treatment fluids, and more particularly totreatment fluids that comprise a zirconium isopropylamine crosslinkingagent and associated methods.

A variety of subterranean treatments using crosslinked treatment fluidshave been developed. One subterranean treatment that uses a crosslinkedtreatment fluid for stimulating production from a subterranean formationis a fracturing treatment. Fracturing treatments generally involvepumping a crosslinked treatment fluid (e.g., a fracturing fluid) into asubterranean formation at a pressure sufficient to create or enhance oneor more fractures in the subterranean formation. The fracturing fluidgenerally has a viscosity that is sufficient to suspend proppantparticulates and to place the proppant particulates in fractures, interalia, to maintain the integrity of those fractures once the hydraulicpressure is released. Once at least one fracture is created and theproppant particulates are substantially in place, the viscosity of thefracturing fluid usually is reduced, and the fluid may be recovered fromthe formation. Other treatments that use crosslinked treatment fluidsinclude, but are not limited to, sand control treatments (e.g., gravelpacking), drilling operations, polymer floods, and forming temporaryplugs or blocks in subterranean formations, and the like.

Crosslinked treatment fluids generally comprise an aqueous fluid and acrosslinked gelling agent, wherein the crosslinked gelling agent may bethe reaction product of a reaction that comprises a gelling agent and acrosslinking agent. This reaction between the gelling agent and thecrosslinking agent is commonly referred to as “crosslinking.”Preparation of these crosslinked treatment fluids typically involvescombining the aqueous fluid with the gelling agent. An optional bufferalso may be included to provide an appropriate pH for hydration of thegelling agent and crosslinking. Next, a crosslinking agent may added forcrosslinking one or more gelling agent molecules. Generally, thecrosslinking may occur very slowly and/or not at all while the treatmentfluid is at or below ambient temperature. As used herein, “ambienttemperature” refers to a moderate temperature range normally encounteredon the surface. For instance, certain crosslinking agents, such aszirconium lactate, may require temperatures greater than about 85° F. toabout 90° F. to initiate crosslinking.

After preparation, the treatment fluid may be placed into a subterraneanformation through a well bore. Because most subterranean formations arerelatively hot, e.g., having temperatures in the range of from about100° F. to about 400° F., the treatment fluid may be heated as it passesthrough the well bore and into the subterranean formation. As thetreatment fluid heats to temperatures greater than ambient temperatures,crosslinking may occur to form a crosslinked treatment fluid that mayhave a desired viscosity for a particular application (e.g., proppanttransport). Treatment fluids, such as those described above, may bedescribed as delayed crosslinking aqueous gels because crosslinking doesnot occur or occurs very slowly prior to introduction of the treatmentfluid into the well bore. An example of a delayed crosslinking aqueousgel comprises an organic carboxylated gelling agent, an aqueous fluid, abuffer (capable of maintaining the pH of the fluid at about 5 or above),and a zirconium IV-containing crosslinking agent.

However, in some instances, the aqueous fluid used to form the gelledtreatment fluids may be relatively cool (e.g., below about 70° F.) andmay even have temperatures as low as about 35° F. Where these relativelycool aqueous fluids are used, the formation temperatures may not besufficient to heat the gelled treatment fluids to temperatures suitablefor crosslinking while the gelled treatment fluids are resident in thewell bore. If these temperatures are not reached, the gelled treatmentfluids may be introduced into the subterranean formation with little orno crosslinking, and thus the gelled treatment fluids may not haveviscosities sufficient for the particular applications. This problem maybe particularly apparent in relatively shallow wells where the time thegelled treatment fluid is resident in the well bore may be short whencompared to deeper wells.

SUMMARY

The present invention relates generally to the treatment of subterraneanformations with crosslinked treatment fluids, and more particularly totreatment fluids that comprise a zirconium isopropylamine crosslinkingagent and associated methods.

An embodiment of the present invention provides a treatment fluid. In anexample of such a treatment fluid, the treatment fluid of the presentinvention may comprise an aqueous fluid, a gelling agent, and azirconium triisopropylamine crosslinking agent. In another example ofsuch a treatment fluid, the treatment fluid of the present invention maycomprise an aqueous fluid; a buffer; a clay control agent; an organiccarboxylated gelling agent; a zirconium triisopropylamine crosslinkingagent; and a Zirconium IV-containing crosslinking agent; wherein thetreatment fluid has a pH in the range of from about 4 to about 6.

Another embodiment of the present invention provides a crosslinkingagent that may comprise a zirconium triisopropylamine crosslinkingagent, and a zirconium IV-containing crosslinking agent.

The features and advantages of the present invention will be apparent tothose skilled in the art. While numerous changes may be made by thoseskilled in the art, such changes are within the spirit of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These drawings illustrate certain aspects of some of the embodiments ofthe present invention and should not be used to limit or define theinvention.

FIG. 1 is a plot of temperature and viscosity versus time as measuredusing a Fann® Model 50 viscometer for sample fluids in accordance withone embodiment of the present invention and control sample fluids.

FIG. 2 is a plot of temperature and viscosity versus time as measuredusing a Fann® Model 50 viscometer for a sample fluid in accordance withone embodiment of the present invention and a control sample fluid.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention relates generally to the treatment of subterraneanformations with crosslinked treatment fluids, and more particularly totreatment fluids that comprise a zirconium isopropylamine crosslinkingagent and associated methods.

The treatment fluids of the present invention generally comprise anaqueous fluid, a gelling agent, and a zirconium isopropylaminecrosslinking agent. Under the appropriate conditions (e.g., pH,temperature, etc.), crosslinking may occur between at least a portion ofthe gelling agent and at least a portion of the zirconium isopropylaminecrosslinking agent to form an at least partially crosslinked gellingagent. In some embodiments, a second crosslinking agent may be includedin the treatment fluids of the present invention in addition to thezirconium isopropylamine crosslinking agent. Additional additives may beincluded in the treatment fluid as desired by one skilled in the art,with the benefit of this disclosure, dependent on the particularapplication. Such additives may include, but are not limited to,buffers, clay control agents, gases, foaming agents, delayed gelbreakers, and a variety of other suitable additives.

Suitable aqueous fluids used to form the treatment fluids of the presentinvention include, but are not limited to, saltwater, brines, seawater,freshwater. Generally, the aqueous fluid may be from any source,provided that it does not contain components that may adversely affectother components in the treatment fluids of the present invention.

A variety of gelling agents can be used in conjunction with the methodsand compositions of the present invention, including, but not limitedto, hydratable polymers that contain one or more functional groups suchas hydroxyl, cis-hydroxyl, carboxylic acids, derivatives of carboxylicacids, sulfate, sulfonate, phosphate, phosphonate, amino, or amide.Suitable gelling agents may comprise polymers, synthetic polymers, or acombination thereof. In certain embodiments, suitable gelling agents maycomprise polysaccharides, and derivatives thereof that contain one ormore of these monosaccharide units: galactose, mannose, glucoside,glucose, xylose, arabinose, fructose, glucuronic acid, or pyranosylsulfate. Examples of suitable polysaccharides include, but are notlimited to, guar gum and derivatives thereof, such as hydroxyethyl guar,hydroxypropyl guar, carboxymethyl guar, carboxymethylhydroxyethyl guar,and carboxymethylhydroxypropyl guar (“CMHPG”); and a cellulose or aderivative thereof, such as hydroxyethyl cellulose,carboxyethylcellulose, carboxymethylcellulose, andcarboxymethylhydroxyethylcellulose; and combinations thereof. In certainembodiments, the gelling agents comprise an organic carboxylated gellingagent, such as CMHPG. In certain embodiments, the derivatized celluloseis a cellulose grafted with an allyl or a vinyl monomer, such as thosedisclosed in U.S. Pat. Nos. 4,982,793; 5,067,565; and 5,122,549, therelevant disclosures of which are incorporated herein by reference.Additionally, synthetic polymers and copolymers that contain theabove-mentioned functional groups may be used. Examples of suchsynthetic polymers include, but are not limited to, polyacrylate,polymethacrylate, polyacrylamide, polyvinyl alcohol, andpolyvinylpyrrolidone, and derivatives thereof. The gelling agents listedabove may be included in the treatments fluids of the present inventionseparately or in combination.

Suitable gelling agents may be present in the treatment fluids of thepresent invention in an amount sufficient to provide the desiredviscosity. In some embodiments, the gelling agents may be present in thetreatment fluids of the present invention in an amount in the range offrom about 0.01% to about 5% by weight of the aqueous fluid. In certainembodiments, the gelling agents may be present in the treatment fluidsof the present invention in an amount in the range of from about 0.01%to about 2% by weight of the aqueous fluid.

The zirconium isopropylamine crosslinking agents useful in the presentinvention may be capable of initiating crosslinking of the gelling agentin the treatment fluids of the present invention at temperatures belowabout 70° F. In certain embodiments, the zirconium isopropylaminecrosslinking agents may be capable of initiating crosslinking attemperatures below about 60° F. And in certain embodiments, thezirconium isopropylamine crosslinking agents may be capable ofinitiating crosslinking at temperatures down to about 35° F.

The zirconium isopropylamine crosslinking agents contain at least onezirconium IV ion that is capable of crosslinking at least two gellingagent molecules. Suitable isopropylamine crosslinking agents include,but are not limited to, zirconium triisopropylamine, zirconiumtriisopropylamine lactate, zirconium diisopropylamine, and zirconiumdiisopropylamine lactate, and derivatives thereof and combinationsthereof. It has been found that the use of zirconium triisopropylamineas a crosslinking agent can initiate crosslinking at low temperatures(e.g., down to about 35° F.). Moreover, the zirconium isopropylaminecrosslinking agents useful in the present invention may be capable ofinitiating crosslinking under relatively high salt concentrations. Incertain embodiments, a zirconium isopropylamine crosslinking agentuseful in the present invention has been show to produce a crosslinkedtreatment fluid at a pH between about 4 and about 6 while at 50° F. andin the presence of about 7% KCl.

The zirconium isopropylamine crosslinking agents generally are presentin the treatment fluids of the present invention, among other things, toprovide the desired degree of crosslinking between gelling agentmolecules. In certain embodiments, the zirconium isopropylaminecrosslinking agents generally may be present in an amount in the rangeof from about 0.001% to about 10% by weight of the aqueous fluid. Incertain embodiments, the zirconium isopropylamine crosslinking agentsmay be present in the treatment fluids of the present invention in anamount in the range of from about 0.01% to about 2% by weight of theaqueous fluid. Individuals skilled in the art, with the benefit of thisdisclosure, will recognize the exact type and amount of crosslinkingagent to use depending on a number of factors, such as the specificgelling agent, desired viscosity, and formation conditions.

The treatment fluids of the present invention optionally may comprise abuffer. Buffers may be included in the treatment fluids of the presentinvention to provide a desired pH, for example, a pH suitable forcrosslinking and/or hydration of the gelling agent. In certainembodiments, the buffer should be capable of maintaining the treatmentfluids of the present invention at a pH of between about 4 and about 12.And in certain embodiments, the buffer should be capable of maintainingthe pH between about 4 and about 6. One skilled in the art willrecognize that a number of suitable buffers may be used to accomplishthis task, such as sodium acetate, ammonium acetate, acetic acid, sodiumcarbonate, potassium carbonate, sodium bicarbonate, potassiumbicarbonate, sodium or potassium diacetate, sodium hydroxide, potassiumhydroxide, and lithium hydroxide, and combinations thereof andderivatives thereof. In certain embodiments, the buffer comprises amixture of acetic acid and sodium carbonate. In certain embodiments, thebuffer comprises a mixture of acetic acid and ammonium acetate.

Generally, the buffer may be present in the treatment fluids of thepresent invention in an amount sufficient to maintain the pH in, oradjust the pH to, a desired value or range. In certain embodiments, thebuffer may be present in the treatment fluids of the present inventionin an amount in the range of from about 0.001% to about 1% by weight ofthe aqueous fluid.

In some embodiments, a second crosslinking agent may be included in thetreatment fluids of the present invention in addition to the zirconiumisopropylamine crosslinking agent. The second crosslinking agentgenerally comprises at least one ion that is capable of crosslinking atleast two gelling agent molecules. Examples of suitable crosslinkingagents include, but are not limited to, compounds that can supply boronions (such as, for example, boric acid, disodium octaboratetetrahydrate, sodium diborate, pentaborates, ulexite and colemanite);compounds that can supply zirconium IV ions (such as, for example,zirconium lactate, zirconium lactate triethanolamine, zirconiumcarbonate, zirconium acetylacetonate, zirconium malate, zirconiumcitrate, and polyhydroxy complexes of zirconium); compounds that cansupply titanium IV ions (such as, for example, titanium lactate,titanium malate, titanium citrate, titanium ammonium lactate,polyhydroxy complexes of titanium, titanium triethanolamine, andtitanium acetylacetonate); aluminum compounds (such as, for example,aluminum lactate or aluminum citrate); antimony compounds; chromiumcompounds; iron compounds; copper compounds; or zinc compounds; or acombination thereof or a derivative thereof. In certain embodiments, thesecond crosslinking agent comprises a compound that can supply zirconiumIV ions, such as a zirconium IV-containing crosslinking agent. Anexample of a suitable polyhydroxy complex of zirconium is described inU.S. Pat. No. 4,460,751, the relevant disclosure of which isincorporated herein by reference. Where a second crosslinking agent isused in addition to the zirconium isopropylamine crosslinking agent, thezirconium isopropylamine crosslinking may be used, in some embodiments,as an accelerant, for example, if the aqueous fluid is at relatively lowtemperatures (e.g., less than about 70° F.), so that the zirconiumisopropylamine crosslinking agent initiates crosslinking at temperaturesless than 70° F.

The second crosslinking agent generally may be present in the treatmentfluids of the present invention in an amount sufficient to provide,among other things, the desired degree of crosslinking between gellingagent molecules. In certain embodiments, the second crosslinking agentmay be present in an amount in the range from about 0.001% to about 10%by weight of the aqueous fluid. In certain embodiments, the secondcrosslinking agent may be present in the treatment fluids of the presentinvention in an amount in the range from about 0.01% to about 1% byweight of the aqueous fluid. Individuals skilled in the art, with thebenefit of this disclosure, will recognize the exact type and amount ofthe second crosslinking agent to use depending on a number of factors,such as the specific gelling agent, desired viscosity, and formationconditions.

Further, the treatment fluids of the present invention optionally may befoamed using a suitable gas (such as carbon dioxide, air, or nitrogen,or a combination thereof) and a foaming agent. Suitable foaming agents,include, but are not limited to, cationic, anionic, nonionic, oramphoteric surfactants, such as, for example, betaines, sulfated orsulfonated alkoxylates, alkyl quaternary amines, alkoxylated linearalcohols, alkyl sulfonates, alkyl aryl sulfonates, alkyl arylalkoxylates, amine oxides, and C₁₀-C₂₀ alkyldiphenyl ether sulfonates,and combinations thereof. The particular foaming agent employed willdepend upon the type of formation which is to be fractured, thetreatment fluid chosen, and the percentage of gas in the final foam. Incertain embodiments, the foaming agent may be mixed with the treatmentfluid of the present invention before the gas is added to facilitateuniform mixing and to assist in stabilizing the two phase structure ofthe foam. One of ordinary skill in the art, with the benefit of thisdisclosure, will be able to select the appropriate amount and type offoaming agent and gas for a particular application.

The treatment fluids of the present invention may further comprise adelayed gel breaker such as enzyme, oxidizing, acid, ortemperature-activated gel breakers. Gel breakers may be used to reducethe viscosity of an aqueous gel once a subterranean treatment issubstantially complete. In certain embodiments, the gel breaker used maybe present in the treatment fluids of the present invention in an amountin the range of from about 0.05% to about 10% by weight of the gellingagent.

Individuals skilled in the art, with the benefit of this disclosure,will recognize that additional additives may be included in thetreatment fluids of the present invention as desired for a particularapplication. Such additives may include, but are not limited to,proppant particulates, clay control agents, corrosion inhibitors,biocides, friction reducers, gel stabilizers, fluid loss controladditives, bactericides, and surfactants, and combinations thereof.Suitable clay control agents include, but are not limited to, potassiumchloride, sodium chloride, and tetramethyl ammonium chloride, andcombinations thereof and derivatives thereof.

An example of a treatment fluid of the present invention comprises anaqueous fluid having a temperature of less than about 70° F., CMHPG inan amount in the range of from about 0.1% to about 1% by weight of theaqueous fluid, a zirconium triisopropylamine crosslinking agent in anamount in the range of from about 0.01% to about 2% by weight of theaqueous fluid, a polyhydroxy complex of zirconium in an amount in therange of from about 0.005% to about 0.5% by weight of the aqueous fluid,a mixture of acetic acid and ammonium acetate in an amount in the rangeof from about 0.005% to about 0.1% by weight of the aqueous fluid, andpotassium chloride in an amount of about 7% by weight of the aqueousfluid, wherein the treatment fluid has pH in the range of from about 4to about 6.

The treatment fluids of the present invention may be prepared using anysuitable methodology. In one embodiment, preparation of a particulartreatment fluid may comprise admixing a gelling agent with an aqueousfluid, combining a buffer with the resulting fluid to adjust and/ormaintain the pH at a desired level for crosslinking and/or hydration ofthe gelling agent, and then combining a zirconium isopropylaminecrosslinking agent with the resulting fluid. The mixing of the zirconiumisopropylamine crosslinking agent and/or the second crosslinking agentinto the treatment fluid may be performed using any suitablemethodology. In some embodiments, the zirconium isopropylaminecrosslinking agent and/or the second crosslinking agent may be combinedinto the treatment fluid “on the fly,” for example the crosslinkingagents may be injected into a stream of the treatment fluid comprisingthe aqueous fluid and the gelling agent during pumping. Other additives,such as those described above, may combined with the treatment fluid ofthe present invention as desired for a particular application.

The treatment fluids may be used for carrying out a variety ofsubterranean treatments, where a crosslinked treatment fluid may beused, including, but not limited to, fracturing treatments, sand controltreatments (e.g., gravel packing), polymer floods, and forming temporaryplugs or blocks in subterranean formations, and the like. In someembodiments, the treatment fluids of the present invention may be usedin treating a subterranean formation. An example of such a subterraneantreating method comprises: providing a treatment fluid of the presentinvention that comprises an aqueous fluid, a gelling agent, and azirconium isopropylamine crosslinking agent; and introducing thetreatment fluid into a well bore that penetrates a subterraneanformation. Crosslinking may occur between at least a portion of thegelling agent and at least a portion of the zirconium isopropylaminecrosslinking agent to form at least one crosslink in the gelling agent.In some embodiments, the treatment fluid may contact the subterraneanformation at or above a pressure sufficient to create or enhance one ormore fractures in at least a portion of the subterranean formation.

In certain embodiments, the treatment fluids of the present inventionmay be used in subterranean treatments, wherein the aqueous fluidavailable for use is relatively cool (e.g., less than about 70° F.). Anexample of such a subterranean treatment method comprises: providing atreatment fluid having a temperature of less than about 70° F., thetreatment fluid comprising an aqueous fluid, a gelling agent, and azirconium isopropylamine crosslinking agent; allowing at least onecrosslink to form in the gelling agent while the treatment fluid has atemperature of less than about 70° F. through a reaction that comprisesat least a portion of the gelling agent and at least a portion of thezirconium isopropylamine crosslinking agent; and introducing thetreatment fluid into a well bore that penetrates a subterraneanformation.

The crosslinking may occur, under the appropriate conditions (e.g., pH,temperature, etc.), between at least a portion of the gelling agent andat least a portion of the zirconium isopropylamine crosslinking agent toform at least one crosslink in the gelling agent. In certainembodiments, the crosslinking begins within a few seconds afterpreparation of the treatment fluid. In certain embodiments, thecrosslinking begins after the treatment fluid has been introduced intothe well bore. In certain embodiments, the crosslinking may beginshortly after preparation of a particular treatment fluid of the presentinvention and continue after the treatment fluid has been introducedinto the well bore. In some embodiments, the treatment fluid maycomprise a second crosslinking agent so that additional crosslinking mayoccur, for example, crosslinking may occur between at least a portion ofthe second crosslinking agent and additional portions of the gellingagent to form additional crosslinked gelling agent. This crosslinkingcomprising the gelling agent and the second crosslinking agent may occurafter the treatment fluid, in certain embodiments, is heated above about70° F. by formation temperatures.

To facilitate a better understanding of the present invention, thefollowing examples of certain aspects of some embodiments are given. Inno way should the following examples be read to limit, or define, thescope of the invention.

EXAMPLES Example 1

Rheological tests were performed using sample fluids prepared asfollows. Four sample fluids (Nos. 1-4) were prepared in a Waring Blendorby dissolving a CMHPG gelling agent in tap water containing 2% KCl byweight. The pH of each sample was adjusted to a pH of about 5 using amixture of acetic acid and ammonium acetate. One or more crosslinkingagents were added to each sample just prior to testing.

Viscosity measurements were made using a Fann® Model 50 viscometerequipped with a 420 spring, a 316SS cup, and a B2X bob. Once prepared,60 ml of the sample fluid at about 75° F. were transferred to the cupand immersed in the preheated bath on the viscometer. The bath waspreheated to 125° F. The cup was set in motion at 106 rpm providing ashear rate of 40 sec⁻¹ on the sample. The viscometer was programmed tomaintain a constant shear rate of 40 sec⁻¹ except when performing ashear rate scan. Shear rate scans were measured at 150, 106, 75, 53, 37,26, and 18 sec⁻¹ with 3 minutes at 40 sec⁻¹ between scans. A plot oftemperature (° F.) and viscosity (cP at 40 sec⁻¹) versus time (min) foreach sample is provided in FIG. 1.

Sample Fluid No. 1 (control) comprised 25 pounds per thousand gallons(lb/Mgal) of a CMHPG gelling agent, 0.5 gallons per thousand gallons(gal/Mgal) of a zirconium lactate crosslinking agent, 1 gal/Mgal of amixture of acetic acid and ammonium acetate, and 2% KCl by weight. Thissample showed no crosslinking until about 90° F.

Sample Fluid No. 2 (control) comprised 25 lb/Mgal of a CMHPG gellingagent, 0.85 gal/Mgal of a polyhydroxy complex of zirconium, 1 gal/Mgalof a mixture of acetic acid and ammonium acetate, and 2% KCl by weight.This sample showed only a minor degree of crosslinking below 90° F.

Sample Fluid No. 3 comprised 25 lb/Mgal of a CMHPG gelling agent, 0.85gal/Mgal of a polyhydroxy complex of zirconium, 0.1 gal/Mgal of azirconium triisopropylamine crosslinking agent, 1 gal/Mgal of a mixtureof acetic acid and ammonium acetate, and 2% KCl by weight. When thezirconium triisopropylamine was added to the fluid, the initialviscosity at 73° F. increased from about 200 cP to about 400 cP,indicating crosslinking below 90° F.

Sample Fluid No. 4 comprised 25 lb/Mgal of a CMHPG gelling agent, 0.5gal/Mgal of a zirconium triisopropylamine crosslinking agent, 1 gal/Mgalof a mixture of acetic acid and ammonium acetate, and 2% KCl by weight.The initial viscosity of this sample was 1300 cP at 74° F., indicatingcrosslinking below 90° F. Sample Fluid No. 4 showed more shearsensitivity than Sample Fluid Nos. 1-3.

Accordingly, Example 1 indicates that zirconium isopropylaminecrosslinking agents may initiate crosslinking at relatively lowertemperatures than in fluids that do not contain the zirconiumisopropylamine crosslinking agents.

Example 2

Additional rheological tests were performed on several sample fluidsutilizing the same shear rate scanning procedure described above inExample 1. For this series of tests, sample fluids were prepared in aWaring Blendor by dissolving 25 lbs/Mgal of a CMHPG gelling agent in tapwater containing either 2% KCl by weight, 7% KCl by weight, or 2gal/Mgal of a tetramethyl ammonium chloride (“TMAC”) clay control agent.The pH of each sample was adjusted to a pH of about 5 using 1 gal/Mgalof a mixture of acetic acid and ammonium acetate. Just prior to testinga polyhydroxy complex of zirconium (“PHCZ”) and/or a zirconiumtriisopropylamine crosslinking agent was included in each sample invarying amounts. Upon preparation, the viscosity of the samples wasmeasured using the shear rate scanning procedure described in Example 1on the Fann® Model 50 viscometer. The viscosity of each sample at 60minutes and 125° F. is listed in Table 1 below to compare the viscosityof fluid systems containing one or more of the tested crosslinkingagents at stable temperature conditions. The results of this test areindicated in Table 1 below. TABLE 1 Crosslinking Agent Clay ControlAgent Viscosity PHCZ Zr(triisopropylamine) KCl TMAC at 40 sec⁻¹(gal/Mgal) (gal/Mgal) (wt %) (gal/Mgal) (cP) 0.8 0 7 0 250 0.8 0.1 7 0318 0.8 0 2 0 450 0.8 0.1 2 0 505 0 0.5 2 0 470 0.8 0 0 2 660 0.8 0.1 02 775

Accordingly, Example 2 indicates that sample fluids containing both azirconium isopropylamine crosslinking agent and a polyhydroxy complex ofzirconium achieve a higher viscosity at stable temperature conditionswhen compared to sample fluids containing only a polyhydroxy complex ofzirconium.

Example 3

Additional rheological tests were performed on several sample fluidsthat were prepared as follows. Two sample fluids (Nos. 5 and 6) wereprepared in a Waring Blendor by dissolving 25 lbs/Mgal of a CMHPGgelling agent in tap water containing 2 gal/Mgal of a tetramethylammonium chloride clay control agent. The pH of each sample was adjustedto a pH of about 5 using 1 gal/Mgal of a mixture of acetic acid andammonium acetate. Just prior to testing 0.5 gal/Mgal of either azirconium lactate crosslinking agent or a zirconium triisopropylaminecrosslinking agent was added to the sample fluid.

Viscosity measurements were made using a Fann® Model 50 viscometerequipped with a 420 spring, a 316SS cup, and a B2X bob. Prior totesting, the blender jar, sample fluid, bob, and cup were chilled in anice bath at 32° F. 60 ml of the chilled sample fluid were transferred tothe cup and immersed in the ice bath on the viscometer. The temperatureof the cup was allowed to slowly rise. The cup was set in motion at 106rpm providing a shear rate of 40 sec⁻¹ on the sample. The viscometer wasprogrammed to maintain a constant shear rate of 40 sec⁻¹. At about 90minutes and 115 minutes, the ice bath was exchanged for a warm waterbath. A plot of temperature (° F.) and viscosity (cP at 40 sec⁻¹) versustime (min) for each sample is provided in FIG. 2.

Sample Fluid No. 5 (control) comprised 25 lb/Mgal of a CMHPG gellingagent, 0.5 gal/Mgal of a zirconium lactate crosslinking agent, 1gal/Mgal of a mixture of acetic acid and ammonium acetate, and 2gal/Mgal of a tetramethyl ammonium chloride. This sample showed nocrosslinking until the sample temperature reached about 90° F.

Sample Fluid No. 6 comprised 25 lb/Mgal of a CMHPG gelling agent, 0.5gal/Mgal of a zirconium triisopropylamine crosslinking agent, 1 gal/Mgalof a mixture of acetic acid and ammonium acetate, and 2 gal/Mgal of atetramethyl ammonium chloride. This sample showed crosslinking below 40°F.

Accordingly, Example 3 indicates that zirconium isopropylaminecrosslinking agents may initiate crosslinking at relatively lowertemperatures than in fluids that do not contain the zirconiumisopropylamine crosslinking agents.

Example 4

Crosslinking tests were performed on sample fluids that were prepared asfollows. For this series of tests, sample fluids were prepared in aWaring Blendor by dissolving 40 lbs/Mgal of a CMHPG gelling agent in tapwater containing 7% KCl by weight. The pH of each sample was adjusted toa pH of about 5 using a mixture of acetic acid and ammonium acetate inan amount of 1 gal/Mgal. Thereafter, 250 ml of the sample fluid weretransferred to a 500 ml glass blender jar that was placed on a Chandlerblender base, set to turn at 2,200 rpm. The temperature of the jar andthe sample was adjusted as indicated in Table 2 for the vortex closuretests. After placement in the blender jar, one or more crosslinkingagents were added to each sample, and the time to close the vortex andto achieve a static dome, also referred to as rollover, was measured.The type and amount of crosslinking agent included each sample werevaried. The crosslinking agents tested included those that supplyzirconium IV ions and those that supply titanium ions. Next, the samplefluid was transferred to a beaker and heated to 90° F. in a water bathwhile stirring. The qualitative elastic (lipping) character of thesample fluid was observed as the temperature of the sample fluidincreased. The lipping character of each sample fluid was observed attemperature.

The results of this series of test are indicated in Table 2. TABLE 2Crosslinking Agent Vortex Closure Tests Lipping Tests Conc. TemperatureVortex Closure Rollover Temperature Type (wt. %) (° F.) (min:sec)(min:sec) (° F.) Observation Zr Lactate¹ 0.08 75.2 0:05 >3:00  90 VeryWeak Lip Zr Lactate² 0.08 — >10:00  — 91 Weak Lip Zr(ammonium acetate)0.08 77.5 0:06 ˜1:00  85 Strong-Brittle Ti(ortho ester complex) 0.0877.6 >10:00  — 90 Very Weak Lip Ti Lactate 0.08 78 >10:00  — 90 No LipTi(slurry complex) 0.08 78.5 >10:00  — 90 No Lip Zr (Al Lactate) 0.0875.2 2:00 ˜10:00  90 Weak Lip Zr(diisopropylamine) 0.08 74.3 0:06 0:1275 Very Strong Zr(diisopropylamine) 0.08 51 0:15 0:43 56 Weak LipZr(triisopropylamine) 0.08 78.3 0:06 0:08 78 Very StrongZr(triisopropylamine) 0.08 49 0:09 0:27 56 Strong Zr(triisopropylamine)0.08 55 0:11 ˜1:20  60 Weak Lip Zr(triisopropylamine) 0.02 + 48 0:12˜3:00  54 Very Weak Lip Zr(triethanolamine- 0.12 60 Moderate Lipglycolate) 70 Strong Lip¹The Zirconium Lactate used in this sample fluid was CL-23 ™crosslinking agent, a product of Halliburton Energy Services.²The Zirconium Lactate used in this sample fluid was Tyzor ® 217 organictitanate, commercially available from Dupont Specialty Chemicals.

Accordingly, Example 4 indicates that zirconium isopropylaminecrosslinking agents may initiate crosslinking at relatively lowertemperatures than in fluids that do not contain the zirconiumisopropylamine crosslinking agents.

Therefore, the present invention is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Whilenumerous changes may be made by those skilled in the art, such changesare encompassed within the spirit of this invention as defined by theappended claims. The terms in the claims have their plain, ordinarymeaning unless otherwise explicitly and clearly defined by the patentee.

1. A treatment fluid, comprising: an aqueous fluid; a gelling agent; anda zirconium triisopropylamine crosslinking agent.
 2. The treatment fluidof claim 1 wherein the aqueous fluid has a temperature of less thanabout 70° F.
 3. The treatment fluid of claim 1 wherein the aqueous fluidhas a temperature of less than about 60° F.
 4. The treatment fluid ofclaim 1 wherein the gelling agent comprises at least one of thefollowing: a guar gum; hydroxyethyl guar; hydroxypropyl guar;carboxymethyl guar; carboxymethylhydroxyethyl guar;carboxymethylhydroxypropyl guar; a cellulose derivative; hydroxyethylcellulose; carboxyethylcellulose; carboxymethylcellulose;carboxymethylhydroxyethylcellulose; a cellulose grafted with an allyl ora vinyl monomer; polyacrylate; polymethacrylate; polyacrylamide;polyvinyl alcohol; or polyvinylpyrrolidone; or a derivative thereof. 5.The treatment fluid of claim 1 wherein the gelling agent comprises anorganic carboxylated gelling agent.
 6. The treatment fluid of claim 1wherein the gelling agent comprises carboxymethylhydroxypropyl guar. 7.The treatment fluid of claim 1 wherein the zirconium triisopropylaminecrosslinking agent is present in the treatment fluid in an amount in therange of from about 0.01% to about 2% by weight of the aqueous fluid. 8.The treatment fluid of claim 1 wherein the treatment fluid has a pHbetween about 4 and about
 6. 9. The treatment fluid of claim 1 whereinthe treatment fluid further comprises a second crosslinking agent. 10.The treatment fluid of claim 9 wherein the second crosslinking agentcomprises at least one of the following: compounds that can supply boronions; compounds that can supply zirconium IV ions; compounds that cansupply titanium IV ions; aluminum compounds; antimony compounds;chromium compounds; iron compounds; copper compounds; or zinc compounds;or a derivative thereof.
 11. The treatment fluid of claim 1 wherein thetreatment fluid further comprises at least one of the following: abuffer; a clay control agent; a gas; a foaming agent; or a delayed gelbreaker.
 12. The treatment fluid of claim 1 wherein the gelling agentcomprises carboxymethylhydroxypropyl guar; wherein the fluid furthercomprises a zirconium IV-containing crosslinking agent; wherein thefluid further comprises a buffer that comprises a mixture of acetic acidand ammonium acetate; and wherein the fluid further comprises a claycontrol agent.
 13. A treatment fluid, comprising: an aqueous fluid; abuffer; a clay control agent; an organic carboxylated gelling agent; azirconium triisopropylamine crosslinking agent; and a zirconiumIV-containing crosslinking agent; wherein the treatment fluid has a pHin the range of from about 4 to about
 6. 14. The treatment fluid ofclaim 13 wherein the aqueous fluid has a temperature of less than about70° F.
 15. The treatment fluid of claim 13 wherein the zirconiumtriisopropylamine crosslinking agent is present in the treatment fluidin an amount in the range of from about 0.01% to about 2% by weight ofthe aqueous fluid.
 16. The treatment fluid of claim 13 wherein thegelling agent comprises at least one of the following: a guar gum;hydroxyethyl guar; hydroxypropyl guar; carboxymethyl guar;carboxymethylhydroxyethyl guar; carboxymethylhydroxypropyl guar; acellulose derivative; hydroxyethyl cellulose; carboxyethylcellulose;carboxymethylcellulose; carboxymethylhydroxyethylcellulose; a cellulosegrafted with an allyl or a vinyl monomer; polyacrylate;polymethacrylate; polyacrylamide; polyvinyl alcohol; orpolyvinylpyrrolidone; or a derivative thereof.
 17. The treatment fluidof claim 13 wherein the gelling agent comprises an organic carboxylatedgelling agent.
 18. The treatment fluid of claim 13 wherein the gellingagent comprises carboxymethylhydroxypropyl guar.
 19. A crosslinkingagent, comprising: a zirconium triisopropylamine crosslinking agent; anda zirconium IV-containing crosslinking agent.
 20. The crosslinking agentof claim 19 wherein the zirconium IV-containing crosslinking agentcomprises at least one of the following: zirconium lactate; zirconiumlactate triethanolamine; zirconium carbonate; zirconium acetylacetonate;zirconium malate; zirconium citrate; or a polyhydroxy complex ofzirconium.